首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   799篇
  免费   32篇
  国内免费   6篇
测绘学   35篇
大气科学   65篇
地球物理   162篇
地质学   249篇
海洋学   71篇
天文学   180篇
自然地理   75篇
  2020年   12篇
  2019年   10篇
  2018年   6篇
  2017年   22篇
  2016年   21篇
  2015年   25篇
  2014年   17篇
  2013年   27篇
  2012年   15篇
  2011年   38篇
  2010年   21篇
  2009年   40篇
  2008年   36篇
  2007年   27篇
  2006年   29篇
  2005年   16篇
  2004年   18篇
  2003年   12篇
  2002年   33篇
  2001年   18篇
  2000年   22篇
  1999年   18篇
  1998年   13篇
  1997年   17篇
  1996年   9篇
  1995年   14篇
  1994年   7篇
  1993年   6篇
  1992年   8篇
  1990年   6篇
  1989年   7篇
  1988年   12篇
  1987年   7篇
  1986年   10篇
  1985年   13篇
  1984年   18篇
  1983年   8篇
  1982年   23篇
  1981年   11篇
  1980年   14篇
  1979年   21篇
  1978年   17篇
  1977年   14篇
  1976年   9篇
  1975年   15篇
  1974年   14篇
  1973年   9篇
  1972年   8篇
  1971年   5篇
  1966年   5篇
排序方式: 共有837条查询结果,搜索用时 187 毫秒
751.
752.
753.
Four papers were read during the first symposium to be held by the Photogrammetric Society, at the University of Birmingham on 3rd and 4th April. Major General R. LI. Brown examined the staff structure of the organisations engaged upon the photogrammetric production of maps in the United Kingdom. Mr. J. R. Hollwey outlined the syllabus for a new Higher National Certificate in photogrammetry during a session which was devoted to education and qualifications. Subsequently, Professor A. J. van der Weele explained the evolution of the courses at ITC. By way of contrast, Professor E. H. Thompson attempted a forecast of developments in photogrammetry during the next decade. The papers succeeded in initiating prolonged discussion among the 80 members who attended.  相似文献   
754.
The paper describes a new type of photogrammetric plotter based on first order formulae. It differs from other attempts at this, in that all the implications of these formulae are accepted with the three principal consequences that the operator views a model that is free of y-parallax, that all effects of convergence of the pictures, including errors in the vertical scale, are removed and that geometrical errors in the heights do not increase with increasing ground elevations. The principles lead to a robust, cheap plotter.  相似文献   
755.
756.
757.
758.
We report optically stimulated luminescence (OSL) dating results from the Old Cedar midden in St. Joseph Peninsula State Park, located between the Gulf of Mexico and St. Joseph Bay near Port St. Joe, FL, USA. The Old Cedar site (8GU85) is located on top of a relict beach ridge which is actively eroding into St. Joseph Bay. Old Cedar is noted for its conch shell tool assemblage, otherwise rare at northwest Florida archaeological sites, and is believed to have been utilized during the Late Woodland Weeden Island and possibly the Fort Walton periods [Benchley, E.D., Bense, J.A., 2001. Archaeology and history of St. Joseph Peninsula State Park: Phase I investigations. Report of Investigations, No. 89, University of West Florida Archaeology Institute]. After removing surficial erosion deposits, we extracted OSL core samples from both the midden layer and the underlying beach ridge. The resulting OSL age is compared with the age of another beach ridge on St. Joseph Peninsula. We hope that this study will aid in the investigation and conservation of Old Cedar specifically and other Weeden Island sites in the St. Joseph Bay area.  相似文献   
759.
A detailed understanding of channel forming and maintenance processes in mountain streams requires some measurement and/or prediction of bed load transport and sediment mobility. Traditional field based measurements of such processes are problematic because of the high formative discharges characteristic of such streams. The application of Optically Stimulated Luminescence (OSL) dating is proposed here as a new way of determining actual residency times of fine sediments and consequently validating selected predictions for the entrainment of sediment in these streams. Model predictions of sediment mobility for selected step-pool and plane-bed channels in a mountain catchment in south eastern Australia are initially calculated using equations of hydraulic competence and the one-dimensional HEC-RAS model. Results indicate that floods exceeding bankfull with recurrence intervals up to 13 years are competent to mobilise the maximum overlying surface grain sizes at both sites. OSL minimum age model results from 7 samples of well bleached quartz in the fine matrix particles indicate general agreement with selected competence equations. The apparent long (100–1400 y) burial age of most of the mineral quartz, however, suggests that competent flows are not able to flush all subsurface fine-bed material. The depth of maximum bed load exchange (flushing) was limited to ≤ twice the depth of the overlying D90 grain size. Application of OSL in this study provides important insight into the nature of storage and flushing of matrix material in mountain streams.  相似文献   
760.
This article analyzes climate change from the perspective of international politics. In the anarchy of the international system, various cooperation problems have stalled the formation of an effective climate regime at the international level. Obstacles occur at three stages of regime formation: the bargaining stage, the transition stage, and the implementation stage. The importance of the transition stage of cooperation, which takes place between the signing of an agreement and its entry into force, has been overlooked by international relations scholars and is particularly important in the climate case. The article assesses the possibility of applying `adaptive management' principles to climate change as a partial response to these political obstacles. While such an approach has significant appeal given the uncertainty surrounding the human-climate interface, its experimental, top-down characteristics are not politically feasible at the international level. I recommend certain modifications of existing institutions and practices to improve international information sharing and facilitate efficient learning. These changes would serve to promote a decentralized and passive – and thus politically viable – version of adaptive management, an effective approach to dealing with climate change at the global level.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号